Convection Patterns in Liquid Oxide Films on ZrB ₂ –SiC Composites Oxidized at a High Temperature

Abstract

During the high‐temperature oxidation of ZrB 2 –SiC composites, liquid boron oxide (B 2 O 3 ) is formed at the zirconium diboride–zirconium oxide interface and transported through the overlying layer of silica liquid by convection, forming distinct convection cells arranged like the petals of a flower. The convection cells are localized by a viscous fingering phenomenon, as the fluid B 2 O 3 rich liquid solution rises through the viscous silica layer. The upwelling B 2 O 3 rich liquid contains dissolved zirconium dioxide, which deposits in the center of the flower‐like structure as the B 2 O 3 evaporates. The driving force for the B 2 O 3 liquid flow is the volume increase upon oxidation of ZrB 2 . Convective transport of B 2 O 3 liquids suggests a novel mechanism for the high‐temperature oxidation of these materials.